2003-12-27 04:00:00 PDT Washington -- Cattle in other states may have eaten the same contaminated feed that infected a Washington state Holstein with mad cow disease, but investigators who want to track the infection to its source are being confounded by the lack of an organized system that would lead them to the herd where the cow was born, officials said Friday.

The lack of a reliable tracking system, and a complex trail of clues, rumors and red herrings means it could be days or months -- if ever -- before all the links are fully explored, officials said. For a nation already jittery about the Holstein, the expanding investigation could spread worry across the country.

"The epidemiological investigation becomes a tangled web of different possibilities," said W. Ron DeHaven, deputy administrator and chief veterinary officer at the Agriculture Department. "Some of those do lead back to Canada. Some take us into the state of Washington and other states as well."

Also Friday, government regulators announced they were planning to nearly double the number of animals to be tested for mad cow disease before slaughter. And they are considering installing an electronic tracking system that would follow animals from birth to death.

Already, consumers who ate meat that may have come from the sick Holstein are concerned. Grocery stores were shipped ground beef and beef patties from meat that included the infected cow 11 days before a test for mad cow disease came back positive and the meat was recalled. It is not yet known how much of the meat was pulled off grocery shelves or has been consumed.

Five major grocery chains in Oregon and Washington have pulled ground beef from shelves. In Oregon, some of the recalled meat has been accounted for at the wholesale level.

Two facilities in Washington state are now under investigation as transient stops for the Holstein between its birth herd and a Mabton farm, which sent it to the slaughterhouse on Dec. 9, DeHaven said.

The birth herd is where the Holstein was likely infected, and from there infectious links could radiate in multiple directions. Investigators want to track down who supplied the birth herd with infected feed four or five years ago in order to determine whether contaminated feed was also sent to other farms. There are gargantuan challenges in figuring out which other animals ate such infected feed, where they may be now -- and whether they might already be in the domestic and international food supply.

As a result of the discovery of the diseased cow, the USDA says it will nearly double the number of tests conducted during the next fiscal year to about 38,000, up from about 20,600 in the current fiscal year, DeHaven said. If the USDA doubles the number of tests, that would mean about one-tenth of 1 percent -- or one out of a thousand -- of the estimated 35 million cattle that are slaughtered annually in the United States would be tested.

Regulators also plan to revisit a controversial Agriculture Department policy that currently allows non-ambulatory animals into the nation's food supply -- the infected Holstein was a such as "downer" cow. Many food safety advocates and legislative initiatives have unsuccessfully tried to eliminate these animals as a food source.

Officials insist that the nation's food supply is safe and that mad cow disease is unlikely to spread because of FDA regulations put in place in 1997. Those rules are designed to keep cattle from getting infected feed. Compliance with the ban has grown from about 75 percent in 1997 to more than 99 percent today, Sundlof said.

Still, the Washington state Holstein was probably infected after the ban was in place, somewhere between the time it was born, around 1999, and the time it was acquired by Sunny Dene Ranch in Mabton in October 2001. Mad cow disease, or bovine spongiform encephalopathy (BSE), is associated with a fatal brain-wasting disorder in humans called variant Creutzfeld-Jakob disease. Some 154 people have died from the disease, mostly in Britain.

The epidemic is believed to have spread because farmers fed ground-up brain and spinal tissue from infected cows to healthy cattle. In nature, cows do not eat meat. The tainted feed carried deadly prions, misshapen proteins that cause the disease. There is no cure for either mad cow disease or its human variant.

Experts say that even if large numbers of animals ate infected feed, only a minority would likely get sick, but it is difficult to quantify the precise risk for an individual animal.